Anticorrosion allyl sulfonate graft chitosan/graphene oxide nanocomposite material

Abstract

Chitosan derivatives are easily synthesized since their amine-bound glucosamine molecular units allow for the introduction of reactive chemical groups within their linear polymer chains. These compounds acted as green corrosion...

Full text

Showcasing research from Professor Jerzy Szpunar’s
research group, Department of Mechanical Engineering,
College of Engineering, University of Saskatchewan,
Saskatoon, Saskatchewan, Canada.
Anticorrosion allyl sulfonate graft chitosan/graphene oxide
nanocomposite material
Graphene oxide (GO) comprises of a unique graphite layer
nanostructure with oxygen-containing functionalities and
defined segregated sp
2 /sp
3 carbon domains. In this study, a
synthesis route for preparing allyl sulfonate graft chitosan/GO
nanocomposite is introduced. Allyl sulfonate graft chitosan was
first synthesized by reacting chitosan and sodium allylsulfonate
before subsequently being grafted onto GO nanosheets. For the
first time, we shed light on the corrosion-inhibiting properties
of this new nanocomposite against steel degradation from
in-depth electrochemical and surface analytical investigations.
Experimental results reveal its potentials as a component of
anticorrosion surface-treatment formulations.
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Materials
Advances
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ISSN 2633-5409
Volume 2
Number 5
7 March 2021
Pages 1415–1776

Anticorrosion allyl sulfonate graft chitosan/
graphene oxide nanocomposite material
Ubong Eduok, * Enyinnaya Ohaeri and Jerzy Szpunar
Chitosan derivatives are easily synthesized since their amine-bound glucosamine molecular units allow
for the introduction of reactive chemical groups within their polymer chains. These compounds also act
as green corrosion inhibitor molecules for industrial metals with no adverse impact on the environment.
In this stduy, we hereby present a synthesis route for introducing allyl sulfonate within the chitosan (CH)
molecular chain via its amino groups by Michael addition reaction. Allyl sulfonate graft chitosan (CH(S))
was synthesized by a reaction involving CH and allyl sulfonate, catalyzed homogeneously by acetic acid
in alkaline pH using sodium persulfate initiator. CH(S) was subsequently grafted onto graphene oxide
(GO) nanosheets. The resultant organic/inorganic hybrid (CH(S)–GO) nanocomposite was then
characterized using appropriate techniques and utilized as a corrosion inhibitor for an X70 pipeline steel
substrate in a CO
2
saturated NaCl electrolyte at 60 1C. The X70 pipeline steel grade is extensively used
in various oilfield applications. This nanocomposite significantly inhibited corrosion, and this was attributed to
the molecular adsorption and formation of protective polymeric chitosan-GO hybrid nanocomposite films
on the metallic surface. The degree of corrosion inhibition between the CH(S)–GO nanocomposite and its
CH(S) precursor was comparatively investigated; superior surface protection was revealed only in the
presence of the hybrid nanocomposite. The physically adsorbed nanocomposite films on steel contributed
to enhanced surface hydrophobicity due to the prevailing low surface energy GO nanosheets. The CH(S)
copolymer analogue must have promoted corrosion inhibition but the hybrid (CH(S)–GO) polymer
nanocomposite ensured a more compact coverage on steel surfaces, hence was effective as a corrosion
inhibitor. Without this nanocomposite, anodic steel corrosion was significant within the test media due to
irreversible actions of CO
2
induced chloride dissolution episodes. This allyl sulfonate graft chitosan/graphene
oxide nanocomposite material may have a future in oilfield chemistry as a corrosion-inhibitor additive in
surface-treatment formulations.
1. Introduction
Most grades of steel are utilized in constructing auto parts in
automotive industries as well as in fabricating transportation
lines and storage structures for oil–gas fluids in petroleum
industries.
1
The applications of steel materials are enormous in
both domestic and industrial spheres, however, their usage is
significantly affected by corrosion. Protecting steel materials
against corrosion has become vital for safeguarding the safety
of steel structures and reducing the cost involved in overall
repairs.
2
To mitigate corrosion, there is a need for developing
safe and sustainable strategies for protecting these fabricated
structures. Of the numerous corrosion remediation techniques,
the use of surface-active corrosion inhibitors has become one of
the most applicable tools in controlling the scourge.
1
Corrosion
inhibitor formulations designed for metal surface protection
are made of a combination of organic and inorganic components
capable of forming barrier films needed to inhibit metallic
dissolution by controlling the ingression of corrosion species
within metal/solution interfaces.
3
Most of these inhibitor
components are film-forming polymeric compounds, and they
are effective in protecting the internal walls of steel-based
transport pipelines.
1
As polymers, their effectiveness as
corrosion inhibitor molecules may depend on factors related
to their chemistry (e.g. solubilization) and molecular structures
(e.g. molecular sizes). Both properties foster the adsorption of
these molecules on metal surfaces.
4
Metal/inhibitor interactions
are also linked with the molecule’s compatibility with metal–
surface chemistry and surface charge, while its ability to adsorb
on surfaces may also be linked with the type of corrosive
medium used.
2
Polymeric corrosion inhibitor molecules with heteroatoms
(nitrogen, sulphur, oxygen, phosphorus, etc.) possess high
Cite this: Mater. Adv.,2021,
2, 1621
Department of Mechanical Engineering, College of Engineering,
University of Saskatchewan, 57 Campus Drive, Saskatoon, S7N 5A9, Saskatchewan,
Canada. E-mail: ubong.eduok@usask.ca, ublook@yahoo.com;
Fax: +1 306 966 5427; Tel: +1 306 966 7752
Received 18th August 2020,
Accepted 31st January 2021
DOI: 10.1039/d0ma00613k
rsc.li/materials-advances
2021 The Author(s). Published by the Royal Society of Chemistry Mater. Adv.,2021,2,16211634 | 1621
Materials
Advances
PAPER

electron density clouds that promote surface adsorption while
those with multiple bonds also possess pbonds that act as
adsorption sites.
5
The electronic properties of organic molecules
are fundamental in elucidating their surface activities against
aqueous corrosion of metals,
6–8
since the presence of unoccupied
d-orbital spaces within corroded metals prompts the acceptance
of free electrons from these organic compounds.
5
This leads to
the formation of metal–surface films in the liquid phase.
Unlike the reduced surface coverage imposed by their monomer
analogues, the molecular sizes of polymers ensure wider and
more compact molecular coverages on these surfaces; hence are
more effective corrosion inhibitors.
1
If adsorbed monolayers of
simple polymer films could significantly distort anodic or cathodic,
those of polymer blends and composites would spontaneously
sustain the degree of surface protective against corrosion. This
is due to the synergistic effects of the individual polymer
components. The higher inhibition effects by hybrid polymers
provide multiple active sites of adsorption on charged metallic
surfaces, in turn displacing preabsorbed water molecules. High
molecular-weight polymer inhibitor blends and composites
act as film-forming blankets that cover metallic surfaces,
subsequently making their desorption almost irreversible
compared to their monomers.
1
Recently, our research group
has investigated the use of chitosanic polymer derivatives for
corrosion protection of pipeline steel in various corrosive
media: glucosyloxyethyl acrylate graft chitosan against pipeline
steel corrosion in 1 M HCl,
9
carboxymethyl chitosan grafted
poly(2-methyl-1-vinylimidazole) in CO
2
saturated acidic oilfield
formation water,
10
poly(N-vinyl imidazole) grafted carboxymethyl
chitosan in 1 M HCl,
11
carboxymethyl chitosan grafted poly(2-
methyl-1-vinylimidazole)/cerium molybdate nanocomposite
against biocorrosion in Desulfovibrio ferrophilus culture.
12
In
summary, corrosion inhibition by chitosanic polymers proceeds
upon molecular adsorption of metallic surfaces and this is
followed by subsequent passive film formation as corrosion is
inhibited.
There may be several limitations with the use of these
polymers; one of the most outstanding could be linked with
limitations of structural flexibility and metal–surface cohesive
bonding.
1
However, with the incorporation of inorganic metal
nanoparticles, the resultant film-forming hybrid polymer nano-
composites possessing versatile and tunable physicomechanical
and chemical properties act as bridges between macro and
hybrid nanostructures.
2
These new nanocomposites possess
unique solution chemistries with aqueous dispersibility capable
of metal adsorption. The presence of metal nanoparticles within
these composites leads to enhanced corrosion resistance, unique
solution stability and surface-active properties (e.g. hydrophobicity)
that are not observed in normal polymers. The protective
performance of several chitosanic nanocomposite systems
incorporated with the following nanoparticles has been
reported: Co/SnS
2
,
13
Ag,
14,15
graphene oxide (GO),
16
ZnO/GO
nano-hybrids,
17
and Fe
3
O
4
,
18
to mention but a few. In the
present study, the allyl sulfonate graft chitosan/graphene oxide
nanocomposite (CH(S)–GO) was used as a corrosion inhibitor
for pipeline steel corrosion in CO
2
saturated NaCl medium at
60 1C. This novel CH(S)–GO nanocomposite was synthesized by
grafting allyl sulfonate graft chitosan (CH(S)) onto graphene
oxide nanosheets. CH(S) was initially synthesized by an acetic
acid catalyzed reaction involving chitosan (CHS) and allyl
sulfonate precursors in alkaline pH. This is a coupling reaction
between the amine functional chitosanic backbone and
double-bond end-groups of reactive allyl sulfonate molecules.
The innovation in the present study is the synthesis and
corrosion-inhibition application of this new CH(S)–GO nano-
composite. Since molecular weights of adsorbing corrosion-
inhibiting films directly contribute to enhanced inhibition,
16
this allyl sulfonate graft chitosan copolymer was chosen for the
present study to foster metal protection due to its size.
High-molecular weight polymers of this nature are known for
their enhanced metal–surface protection via physical adsorption,
and so this is why CH(S)–GO in the present study is an
advantage.
15,16
The reason for the choice of this graft copolymer
could also be linked with the presence of sulphur atoms on the
graft allyl sulfonate moiety that would foster strong metal–
surfacebinding,inturnpromotingenhanced corrosion inhibition.
This is one of the major advantages of using this graft copolymer
cross-linked with allyl sulfonate, compared to straight-chain
chitosan derivatives with no such side chains. The presence of
functional oxygen heteroatoms from the chitosan ring also
provides good adsorption affinity for steel-surface binding
toward improved corrosion inhibition efficiency.
16
Infusion of
GO nanoparticles within the polymer matrices further
enhances the anticorrosion performances of the nano-
composites due to their hydrophobicity and high surface
area.
16
The advancement in the present study is the GO
modification of the chitosan polymer matrix for superior
rigidity and hydrophobicity toward reinforced barrier properties.
The resultant anticorrosion film from this nanocomposite would
impede more diffusion paths of corrosive species as well as
charge transfer between localized anodic and cathodic sites.
15,16
With graphene oxide derivatives, corrosion inhibition is
enhanced due to the factors related to some of their unique
physical and chemical properties (e.g. significantly low surface
energy, superhydrophobicity, high chemical resistance, thermal
conductivity and mechanical strength).
19–22
In aqueous phases,
GO is able to form insoluble hydrophobic layers that further
protect metal surfaces while also contributing to stable corrosion
performance by virtue of its surface-bound chemical groups
(e.g. hydroxyl, carboxyl, epoxides, and carbonyl groups).
16,21,22
GO is a reliable precursor for most organically modified nano-
materials with potential for sustainable corrosion inhibition.
The allyl sulfonate graft chitosan/GO nanocomposite, like
most chitosan derivatives, is an eco-friendly corrosion inhibitor
compared to the toxic nitrate, dichromate and chromate-based
anticorrosion formulations. The novel properties of this hybrid
material span between those of the polymeric chitosan and the
incorporated inorganic GO component.
2
Generally, chitosan
derivatives are benign, safe and effective corrosion inhibitor
molecules that leave no adverse residual byproduct that
impacts the environment. They are more effective and easier
to synthesize since their amine-bound glucosamine molecular
1622 |Mater. Adv.,2021,2,16211634 2021 The Author(s). Published by the Royal Society of Chemistry
Paper Materials Advances

units allow for introduction of useful reactive chemical groups
within these molecules.
10
The reason for conducting the present investigation in CO
2
saturated media could be linked with the present corrosion
issues involving carbon dioxide gas (CO
2
), a causative corrosion
agent for pipeline steel. CO
2
is also a serious corrosive gas
whose intermediate carbonic aicd product that significantly
contributes to anodic degradation. CO
2
is a byproduct of most
chemical processes in the oil and gas industries. Corrosion of
pipeline steel is severe in CO
2
saturated brine media at acid pH,
and this happens mostly when steel structures (e.g. pipeline
materials) are exposed to chloride enriched oilfield formation
media.
23
These corrosion episodes increase during the trans-
portation of fluids under heat-generating hydrodynamic
conditions in product transportation pipeline assembly; these
events also lead to the erosion of their internal walls. Left
unchecked and untreated, corrosion leads to damaged
transportation pipelines and loss of contents (by leakages). In
order to avoid these economic losses, the production cost is
heavily supported by service maintenance operations involving
reliable corrosion protection programs in which the use of
corrosion inhibitors is a major content.
10
This carbon-based
GO nanomaterial was introduced in this study in order to
institute reduced wetness to the adsorbed protective nano-
composite films on steel during the corrosion inhibition process.
The use of GO in surface science investigation like this one has
attracted considerable attention due to its unique nanostructure
as it comprises of segregated sp
2
carbon domains as unique
functionalities. It is also easily reduced by catalytic nitrile
oxidation.
24
2. Materials and methods
2.1. Reagents and chemicals
200 kDa molecular-mass chitosan (CH) was commercially purchased
from Sigma Aldrich. Its degree of deacetylation stood at 88%.
Sodium allyl sulfonate (C
3
H
5
NaO
3
S, 99%), sodium hydroxide
(NaOH, Z98%), acetone (Z99.9%), sodium persulfate (Z99%),
hydrazine monohydrate (98%) and reduced graphene oxide
(rGO) were also purchased from Sigma Aldrich. Acetic acid
(Z99.7%) and sodium persulfate (Na
2
S
2
O
8
,Z99%) were utilized
as the catalyst and initiator, respectively; both were purchased
from the same outlet. All reagents were used as purchased
without purification.
2.2. Pipeline steel material
The metallic test substrate used in this study was a pipeline
steel material belonging to a class of thermomechanically
processed API (American Institute of Petroleum) 5L X70 grade
donated by EVRAZ North America. The chemical composition
of this steel is as follows: C: 0.047, Mn: 1.65, S: 0.0018, P: 0.009,
Si: 0.18, Cu: 0.29, Ni: 0.07, Cr: 0.06, V: 0.001, Nb: 0.073, Mo:
0.247, Sn: 0.01, Al: 0.044, Ca: 0.0014, B: 0.0001, Ti: 0.022, N:
0.0099, O: 0.003, and Fe: balance. For the corrosion test, this
metal was cut into small strips of 3 cm 3cm1cm
dimension before masking them to define a one centimeter
squared geometric area. The microstructure of pipeline steel
was established by the EBSD (electron backscatter diffraction)
approach. A piece of steel specimen was machined out of the
plate. Then, its surface RD – TD plane was mounted and
polished with 500, 800, 1000, 1200, 2000 and 4000 mm abrasive
papers. A mirror-like finish was achieved by further chemo-
mechanical polishing in a colloidal silica suspension for 12 h.
Electron diffraction patterns were collected using a field
emission Hitachi SU6600 scanning electron microscope (SEM)
that was fitted with an EBSD detector. An accelerating voltage of
30 kV and a step size of 0.14 were applied during scanning. The
results were collected with the aid of Oxford Instrument’s
AZTEC 2.0 software, and later post-processed on the channel
5 software.
2.3. Preparation of allyl sulfonate graft chitosan
The synthesis of allyl sulfonate graft chitosan (CH(S)) was
carried out by an acetic acid (CH
3
COOH) catalyzed reaction
with a chitosan (CH) precursor in alkaline pH. About 2 g of CH
was completely dissolved in 2 g of CH
3
COOH in 200 mL of
water before adding premixed solution of 5 g of sodium
allylsulfonate (C
3
H
5
NaO
3
S) and 1 g of persulfate (Na
2
S
2
O
8
).
This suspension was continuously stirred for 1 h at 45 1C.
The reaction was allowed to proceed at the same temperature
for 48 h in a vacuum (as presented in Figure 1) after increasing
the medium pH to 8 using 20% NaOH solution. Significant
amounts of water and excess unreacted reagents were evaporated
in a vacuum, leaving 80 mL of the product. It was then mixed
with 500 mL of acetone to remove the unreacted C
3
H
5
NaO
3
S
reactant. The resultant precipitate was repeatedly washed and
filtered accordingly before finally drying overnight in a vacuum
oven at 40 1C.
2.4. Preparation of the allyl sulfonate graft chitosan/graphene
oxide nanocomposite
CH(S) was later grafted onto graphene oxide nanosheets via
chemical grafting. This process was initiated after dispersing
reduced graphene oxide (rGO) in water. The pre-washed CH(S)
product was dissolved in 2 g of CH
3
COOH in 200 mL of water
before dispersing graphene oxide pigments within the acidified
CH hydrogel suspension. The medium was vigorously stirred
(850 rpm) for 15 min at 40 1C (pH increased to 8 with ammonia
solution). The medium was then sonicated for 30 min, filtered
and then sparged with nitrogen gas. Before this, about 10 mL of
hydrazine solution was slowly added during stirring, heated to
50 1C for 6 h and allowed to cool. The resultant nanocomposite
was later weighed, stored for characterization using appropriate
techniques and used as the corrosion inhibitor in this study.
A similar procedure was reported by Haruna et al.
25
for obtaining
cyclodextrin–GO nanocomposites.
2.5. Characterization of the chitosan precursor and reaction
products
Comparative analyses between the chitosan (CH) precursor,
allyl sulfonate graft chitosan CH(S) and CH(S)–GO solid
2021 The Author(s). Published by the Royal Society of Chemistry Mater. Adv.,2021,2,16211634 | 1623
Materials Advances Paper

powdery products were performed using nuclear magnetic
resonance (NMR) spectroscopy and attenuated total reflection
Fourier transform infra-red spectroscopy (ATR-FTIR). NMR
spectroscopy was conducted using an Avance III HD 600 MHz
NMR spectrometer (Bruker) between both chitosan derivatives
without rGO within the nanocomposites. The FTIR spectra were
collected in transmittance mode after 32 scans from a Bio-RAD
FTS-40 spectrophotometer (Bio-Rad). A comparative XRD analysis
of CH, CH(S), rGO nanosheets and CH(S)–GO nanocomposites
was performed using an X-ray diffractometer (Bruker D8 Discover
XRD diffractometer). This experiment was conducted with CuKa
characteristic radiation while the accompanying spectra present
the 2yangle ranging between 10 and 90 degrees with a
0.02-degree scanning step and 101min
1
scan rate. Thermo-
gravimetric analysis (TGA) experiments were conducted using
5 mg of samples of both materials using a TGA SDT Q600 analyzer
after placing them in Pt crucibles. Weight loss-temperature curves
of these samples were recorded and analysed using appropriate
software from the instrument after analyses in a mixed N
2
/O
2
atmosphere (both placed at 50 mL min
1
flow rate) at 5–20 1Cmin
1
heating rates. Inherent oxidative volatile products generated
during the test were eliminated from the first N
2
flow.
9
The
surface morphologies of both powders were also analyzed using
a SEM at 1 kV acceleration voltage on precoated Au powder
samples (10 nm; Quorum Q150T ES). Raman spectroscopy was
carried out for rGO nanosheets using Renishaw Raman InVia
reflex microscope (Renishaw) using a 514 nm edge laser. The
Brunauer–Emmett–Teller (BET) surface area and nanopore
volume of the rGO nanosheets were also measured using a
BET instrument, Micromeritics ASAP 2020 and a porosimetry
system, respectively. Prior to the BET tests, all test samples were
completely degassed at 50 1C for 4 h in order to completely
remove adsorbed moisture. Nitrogen gas was passed through
the samples throughout the experiments.
2.6. Electrochemical corrosion tests
The electrochemical tests in this study were conducted by
means of a potentiostat/galvanostat/ZRA (Interface 1000,
Gamry Instruments) in a three-electrode set up. A Faraday cage
was also utilized to avoid external interference. The Ag/AgCl
(sat. KCl) was utilized as the reference electrode while platinum
and steel strips were deployed as counter and working electro-
des, respectively. The defined geometric area on each working
electrode to the corrosive electrolyte (approximately 100 cm
3
)
was 10 cm
2
. The corrosive media is this study was CO
2
satu-
rated brine (NaCl) spiked with 3 M acetic acid. This medium
was purged with N
2
for 10 min before saturating it with 99.99%
CO
2
for the duration of the test. The pH of the medium was 2.
To avoid gas loss between each measurement, the CO
2
gas
was bubbled (10 L min
1
) for 2 h each time and maintained
at this pressure at 60 1C in a jacketed MultiPort Corrosion
Cell Kit (Gamry). The frequency range for the electro-
chemical impedance spectroscopy (EIS) measurements was
between 0.1 and 10 000 Hz. EIS measurements were carried
out at 10 mV peak-to-OCP amplitude sinusoidal perturbation;
all measurements were conducted at open circuit potential
(OCP) with reference to the Ag/AgCl (sat. KCl) electrode. The
impedance results collected as EIS spectra were fitted with
appropriate electrical equivalent circuit models in order to
obtain different electrical parameters related to the properties
of each tested system. This was accomplished by means of
EChem Analyst software. Apart from having physical meanings,
the chosen circuit model significantly minimized relative errors
associated with each frequency point and also contributed to
very low chi-squared error (less than 10
4
).
26
This direct-current
test was also performed on each steel coupon after applying a
corrosion potential between 0.25 and 0.25 V at 0.4 mV s
1
sweep rate. The corresponding magnitudes of corrosion current
density ( j
corr
), also regarded as the corrosion rate, were
obtained after Tafel fitting from both anodic and cathodic
polarizations. Each test steel coupon was removed at the end
of the tests and cleaned in accordance with the ASTM G3-89
(2010) standard.
27
2.7. Surface morphological and compositional analyses after
corrosion tests
The corroded steel surfaces exposed to both acid media saturated
with CO
2
gas, with and without CH(S) and CH(S)–GO nano-
composites were investigated by means of scanning electron
microscopy (SEM) and atomic force microscopy (AFM). SEM
analyses were performed using a SU6600 SEM microscope
(Hitachi High-Tech) after a 24 h exposure at 60 1C. All tests were
confirmed by visual surface examinations. SEM analyses were also
complemented by surface topological analyses of molecular
adsorption on steel surfaces. AFM roughness quantification and
image scans of surface areas of interest (10 10 mm) were
performed in intermittent contact mode and at 1 Hz scan rate.
All scans were probed with the aid of a silicon cantilever (whose
properties are enlisted in Table 1), attached to a Model 4500 AFM
instrument (Agilent Technologies). Gwyddion software was
utilized for all post-imaging processing and analyses, including
surface profiling and dimensional analyses of surface features.
X-ray photoelectron spectroscopy (XPS) spectra of these adhering
corrosion inhibitor/corrosion product aggregates were investi-
gated for their chemical compositions. This surface analysis
was conducted with the aid of a Kratos AXIS Supra X-ray Photo-
electron Spectrometer with a monochromatized Al KaX-ray
radiation source. Spectrograms of these surfaces were
collected from a C 1s internal reference with a binding energy
of 285.0 eV. Their peak quantification and further simulations
were conducted using a CasaXPS software, for both wide-scan
anddeconvolutedhigh-resolutionXPSspectrograms.Inorderto
determine the hydrophobicity of each surface, their aqueous con-
tact angles (y
o
w
) were investigated using a DataPhysics Instrument.
Table 1 Properties of the silicon cantilever used in this study
Force constant
Resonant
frequency
Curvature
radius Tip shape
50 N m
1
170 kHz o10 nm Standard/conical
1624 |Mater. Adv.,2021,2,16211634 2021 The Author(s). Published by the Royal Society of Chemistry
Paper Materials Advances

After measurements, the values of y
o
w
for each surface were extra-
polated after surface analyses by the pendant drop method.
3. Results and discussion
3.1. Microstructure analysis of the test steel substrate
The results from the microstructural examination are presented
in Fig. 2. First, it is obvious that the steel structure is made up of
refined grains. The band contrast image shown in Fig. 2(a)
confirms the dominant presence of bainitic-ferrite grains across
the scanned area. Such a decrease in grain size is required to
achieve the necessary strength required in high strength pipeline
steel. The deployment of thermomechanically controlled
processing (TMCP) in the production of steel plate warrants
intense deformation followed by accelerated cooling, which gives
rise to the end microstructure.
28
These authors identified TMCP
as a means of improving the mechanical properties of steel
through grain refinement. This implies that the processing
technique adopted in producing the current pipeline steel
favoured the development of fine grains. Similarly, low angle
grain boundaries (LAGBs) marked in lime colour are seen dis-
persed amongst prominent manifestationofhighanglegrain
boundaries (HAGBs) represented as black lines in Fig. 2(b). Grain
boundaries are categorised with respect to the misorientation
angle (y). The LAGBs are classified within 51oyo151,whilethe
HAGBs include grains with yvalue ranging from 151oyo62.51.
Also, the phase distribution map presented in Fig. 2(c) indicates a
strong presence of body centered cubic (BCC) iron in a ferrite
phase. Insignificant manifestations of face centered cubic (FCC)
iron are red spots, which correspond to the austenite phase. One
can simply say that the steel is primarily made up of BCC iron.
The matching IPF (inverse pole figure) orientation map is
presented in Fig. 2d. Although the grains are randomly oriented,
the [111]||ND grains (blue coloured) are in relatively larger proportion
with slight deviation towards [011]||ND (green coloured). Similar
grain orientation patterns have been established elsewhere in a
previous study on X70 pipeline steel.
29
In addition, the IPF
attached to Fig. 2d clearly shows higher intensity at the [111]
pole compared to the [011] pole. This corroborates the earlier
claim that [111] grains featured more in the scanned area.
However, increased rolling deformations impart a higher degree
of local average misorientation (LAM). According to Fig. 2(e) the
steel comprises of more misoriented grains. The LAM analysis
was performed on grains having yvalues that are less than 51.
In a similar manner, highly deformed grain structures (red
coloured region) are noticeable in Fig. 2(f). The fraction of
the deformed region amounted to 85.4%; whereas the recovered
and recrystallized regions accounted for only 8.3 and 6.4%,
respectively. The microstructure observed in the test material
consists of features that are quite typical of hot rolled steel.
3.2. NMR and FTIR spectroscopy of synthesized allyl
sulfonate graft chitosan copolymers
In the present study, a synthesis route for introducing allylsul-
fonate within chitosan (CH) molecular chain via its amino
groups was presented via Michael addition reaction. Most
importantly, this reaction was chosen in order to exploit the
susceptibility of the sulfonate group to metal–surface interactions
during corrosion inhibition. The final product is an allyl sulfonate
graft chitosan (CH(S)) copolymer with a 90% computed product
yield. It was formed after reacting both precursors via their
chitosanic amino chemical group and the allyl double bonds.
30
The elaborate synthetic formation scheme is presented in Fig. 1.
Before modification with rGO, the resultant amorphous and
fibrous chitosanic powder was characterized using appropriate
spectroscopic techniques. The comparative proton 1H NMR
spectra of this chitosan derivative CH(S) and its CH precursor
are presented in Fig. 3(a and b). Fig. 3(b) depicts the NMR
spectrum of the new allylsulfonate graft chitosan copolymer
derivative. When compared to proton signals of the CH precursor,
the new peaks between 2 and 3.5 ppm could be attributed to
Ha–Hc protons after the substitution of the N-alkylated group to
the amino group by the allyl double bonds. The proton signal of
the –CH
2
group for CH(S) is very intense at 1.89 ppm relative to
CH. A closer view at this spectrum also reveals that a singlet
peak could be consistent with the presence of acetyl proton of the
N-acetylglucosamine (GlcNAc) at 1.85 ppm.
30,31
Apart from the
survival of this acetyl proton (H1), there is also another singlet at
2.98 ppm due to H2 of GlcNAc and N-alkylated GlcNAc groups.
The proton peaks between 3.52 and 3.72 ppm are consistent with
protons H3 to H6.
After grafting CH(S) onto the graphene oxide nanosheets via
chemical grafting, the resultant nanocomposite was characterized
using appropriate techniques. Fig.4(a)depictstheFTIRspectraof
the as-synthesized allyl sulfonate graft chitosan/graphene oxide
(CH(S)–GO) nanocomposite and the CH(S) product as well as its
CHS precursor. Common among thesespectraarestretching
vibration broad envelops of –OH, –NH at 3450 cm
1
and C–H at
2880 cm
1
as well as a glucosamine carbonyl IR peak at
1733 cm
1
from the ester bond. Peaks consistent with glycosidic
C–O–C linkage bonds are located around 1040–1150 cm
1
while
those due to symmetric and asymmetric stretching vibrations of
the glucosamine carbonyl group and OH deformation could be
seen around 1500–1750 cm
1
, respectively.
32,33
There are also
N–H and C–N bending vibration peaks at 1560 and 1500 cm
1
while those at 1380 and 1420 cm
1
are consistent with C–N axial
stretching and N–H deformation, respectively.
34
In comparison
with the spectrum of CH, the IR absorption signal at 2920 cm
1
for the CH(S) spectrum is consistent with the –CH
2
bending
vibration. This is suggestive of complete chemical grafting of
the allylsulfonate chemical group within the chitosanic chain. The
observed IR peaks at 1050 and 1195 cm
1
are also due to the
contributions of the sulfonate group.
30
Since the CH(S)–GO
nanocomposite was incorporated with rGO nanosheets, its
FTIR spectrum shows characteristic peaks consistent with rGO.
Peaks linked with peroxide/epoxy chemical groups and O–H
deformation are found at 957 and 1404 cm
1
, respectively, while
those of alkoxy and epoxy carbonyl stretching vibrations are
located at 1049 and 1227 cm
1
. The presence of these peaks is
due to inherent hydroxyl, carboxylandepoxidechemicalgroups
on the rGO nanosheets.
35
The results of both spectroscopic
2021 The Author(s). Published by the Royal Society of Chemistry Mater. Adv.,2021,2,16211634 | 1625
Materials Advances Paper

techniques reveal a successful grafting of the allylsulfonate
group within the chitosanic molecular chain via its amino groups
via the Michael addition reaction. Secondly, CH(S) grafted
graphene oxide (GO) particles reveal absorption peaks consistent
Fig. 1 Formation scheme for the allyl sulfonate graft chitosan/graphene oxide (CH(S)–GO) nanocomposite from chitosan: allyl sulfonate graft chitosan
CH(S) was synthesized by an acetic-acid catalyzed reaction involving chitosan (CHS) and allyl sulfonate in alkaline pH in the presence of a sodium
persulfate initiator.
Fig. 2 EBSD maps showing (a) band contrast (b) grain boundary character (c) phase map (d) IPF orientation distribution (e) LAM (f) area fraction of
recrystallized, recovered and deformed regions.
Fig. 3
1
H NMR spectra of (a) chitosan (CH) and (b) the synthesized allyl sulfonate graft chitosan (CH(S)) copolymer utilized as a corrosion inhibitor within
the present study (solvent: premixed CD
3
COOD and D
2
O). Broadened peaks are due to inherent interactions between some chitosanic protons.
1626 |Mater. Adv.,2021,2,16211634 2021 The Author(s). Published by the Royal Society of Chemistry
Paper Materials Advances

with both primary components, CH(S) copolymers and GO
nanosheets.
3.3. Characterization of allyl sulfonate graft chitosan/GO
nanocomposites and rGO nanosheets
The XRD patterns of the as-synthesized allyl sulfonate graft
chitosan CH(S), its nanocomposite (CH(S)–GO) and the CH
precursor are depicted in Fig. 4(b). Between these three materials,
their X-ray diffractograms show strong reflection between 2y=20
and 351and a few at 21.31and 22.41, except for pure chitosan
(CH). There are wide peaks between 2y=25and401that could be
ascribed to highly crystalline chitosan (due to the influences of
inter-molecular and extra-molecular hydrogen bonding). There
are resolved diffraction peakslinkedwith002and10reduced
GO planes for the CH(S)–GO nanocomposite between 2y=11and
2y= 42.261, respectively, and this may be indicative of the
prevalence of short-range order within stacked graphene
layers.
36
The observed differences could be attributed to inherent
degrees of crystallinity as a result of reduced GO content and
extra-molecular hydrogen bonding.
30
Apart from the inorganic
content, between CH and its graft copolymer derivatives, the
differencesinfingerprintpeaks(2y) at 21.11and after 401could
be due to varying degrees of crystallinity between these chitosanic
materials. This is consistent with the disruption of the molecular
structure with the presence of sodium allyl sulfonate moieties
grafted to the chitosan polymer chain.
30
These differences are also
reflected in their thermogravimetric (TG) curves depicted in
Fig. 4(c). These curves were recorded under an Ar atmosphere,
and regions of higher weight loss are contributions linked
with the compactness of their organic polymer structures and
inorganic GO content.
9,30
Compared to unmodified chitosan
(CH), the SEM of the as-synthesized CH(S) copolymer shows
differences in fibrous morphology after allyl sulfonate grafting
(Fig.4d).ThesurfacemorphologyoftheCHflakesshowslarger
andagglomeratedparticlesandlessamorphouscomparedto
that of the CH(S) copolymer.
9
Prior to SEM imaging, these
vacuum-dried powdery CH and CH(S) grains were simply placed
on conducting tapes on SEM sample holders with no further
treatments, except for thin film Au coating (10 nm; Quorum
Q150T ES). The presented morphologies are consistent for dried
samples. Solubilization and drying of synthesized CH(S)
powder could have affected its morphology compared to that of
as-received CH.
The surface morphologies and chemical makeup of the
reduced graphene oxide in this study were also investigated
using AFM and SEM techniques as well as ATR-FTIR spectro-
scopy, respectively. After the modification step presented in
section 2.4, the reduced GO nanosheets and CH(S)–GO nano-
composites were evenly dispersed in water at 60 1C. Their
suspension remained stable for several days without the need
Fig. 4 FTIR (a) XRD (b) and TGA (c) curves and SEM micrographs (d) of CH(S) and CHS(S)–GO nanocomposites; inset: SEM of CHS powder of unmodified
chitosan (CH) compared to the as-synthesized allyl sulfonate graft chitosan (CH(S)) and allyl sulfonate graft chitosan/graphene oxide (CH(S)–GO)
nanocomposite.
2021 The Author(s). Published by the Royal Society of Chemistry Mater. Adv.,2021,2,16211634 | 1627
Materials Advances Paper

for capping reagents. The AFM micrographs (Fig. 5a and b)
show distinct monolayers and still preserved individual
nanosheet motifs
37
while the adjacent height profile shows
variations of some surface parameters mapped from the
surface AFM topology (Fig. 5c). The measured thickness in
these nanosheets is between 1 and 1.5 nm and few nm of
lateral dimension. AFM scans were collected in tapping mode
while Gwyddion software was utilized for post-imaging
processing, surface profiling and dimensional analyses of the
rGO nanosheet. Between the ATR-FTIR spectra of both rGO
nanosheets and CH(S)–GO nanocomposites, there are distinct
peaks consistent with CQO stretching and O–H deformation
vibration at 1733 and 1404 cm
1
, respectively. There are also
peaks at 1227 and 1049 cm
1
, attributed to C–O from epoxy and
alkoxy stretching vibrations, respectively, and these chemical
groups are due to inherent residual oxygen, hydroxyl, periphery
carboxyl and epoxide groups on the rGO nanosheet surfaces.
There is also a peak at 957 cm
1
consistent with epoxy (or
peroxide) groups.
38
He et al.
38
have opined that inherent
interactions between hydrogen bonds within these functionalities
further disrupt the p–pstacking between nanosheets in turn,
averting particulate agglomeration. The glucosamine carbonyl IR
peak at 1733 cm
1
and the glycosidic C–O–C linkage bonds are in
the range around 1040–1150 cm
1
.
32,33
The SEM micrographs of
rGO nanosheet powder (Fig. 5e) show rGO nanosheets with folded
and corrugated morphology while allyl sulfonate graft chitosan
copolymerpowdercouldbeobserved infused within rGO sheets
within the nanocomposite (Fig. 5f). Raman and XRD patterns of
rGO nanosheets are also shown in the inset. The first spectrum
shows D mode due to DGO vacancies while the D mode to G mode
ratio (I
D
/I
G
) is more than unity due to the contributions of
hydrazine.
37
On the Raman spectrum, the D band is lined with
the symmetry A1g mode and G band with the E
2g
mode of sp
2
carbon atoms.
37
The BET-derived surface area and pore volume of
these rGO nanosheets were measured to be 3.5581 m
2
g
1
and
0.0244 cm
3
g
1
.
3.4. Examination of inhibition by electrochemical techniques
The EIS technique is a suitable tool for the characterization of
adhering inhibitor layered formations on metal surfaces due to
its ability to probe kinetic controls and transport processes
associated with corrosion.
26
In the present study, EIS was
utilized in studying the electrochemical processes connected
with the dissolution of the steel substrate in the presence of a
hybrid film-forming CH(S)–GO polymer nanocomposite. The
impedance curves for steel substrates in CO
2
saturated NaCl
electrolytes containing different concentrations of nanocomposites
are depicted in Fig. 7(a). These curves are single-loop capacitive
semicircles, and this could be linked with reactions associated
with charge transfers.
9
Wider curves are consistent with con-
centrations of nanocomposites that offered the most inhibition
against steel corrosion, and this could be attributed to the
formation of passive inhibitor films on these metallic
surfaces.
9–11
This trend is also consistent with an increase in
charge transfer resistance (R
ct
) with increasing nanocomposite
concentrations; magnitudes of R
ct
up to 61.4, 214.7, 290.0 and
361.4 Ocm
2
were recorded for 0, 5, 15 and 25 ppm. These
impedance curves were fitted into an appropriate circuit model
(R
soln
(Q
dl
(R
ct
))) and the aforementioned values of R
ct
as well as
other electrochemical parameters were obtained as presented
within the supporting information (Table 2). R
ct
and R
soln
denote the values of resistance associated with the charge
transfer and the acidic solution, respectively. Q
dl
is the constant
phase element (CPE, Y
o
), and it is the capacitance components
Fig. 5 AFM micrographs showing rGO nanosheets (a and b); (c) height profile showing variations of some surface parameters mapped from the surface
AFM topology. Comparative (d) ATR-FTIR spectra and SEM micrographs of reduced GO nanosheet powder (e) and allyl sulfonate graft chitosan/graphene
oxide (CH(S)–GO) nanocomposite powder (f). Inset: Raman and XRD of reduced GO nanosheets; aqueous suspensions (0.1 mg mL
1
rGO and CH(S)–GO
nanocomposites).
1628 |Mater. Adv.,2021,2,16211634 2021 The Author(s). Published by the Royal Society of Chemistry
Paper Materials Advances

introduced to make up for defects within the double layer and
metallic surface.
10
Its impedance is defined as ZCPE ¼1
YoðjoÞa.
Here, the magnitude of j, an imaginary factor, is equal to ffiffiffi
1
p;o
is equivalent to 2pf, where o(rad s
1
) and f(Hz) are angular
and real frequencies. aand Y
o
are associated with the nature of
electroactive species and phase shift, respectively. The magnitudes
of Q
dl
were observed to decrease with the increasing nano-
composite concentration, and this was consistent with the
gathering of passive films that gradually displaced adsorbed
water molecules at the metallic steel surfaces. These physical
surface events isolated the metallic surfaces from further
corrosion. Also, the corrosion inhibition of metallic substrates
is controlled by transient responses of associated reactions at
metal–electrolyte interfaces as well as the presence of adhering
corrosion products/passive inhibitor films.
25
The kinetics of electron transfer during steel corrosion
within this CO
2
saturated NaCl medium after application of
active dissolution potentials was also investigated using the
potentiodynamic polarization technique.
11,21
The polarization
curves for this metal in nanocomposite doped NaCl media are
presented in Fig. 7(b); these results complement those obtained
from the EIS technique. After appropriate theoretical fitting,
the associated Tafel parameters were collected and are presented
in Table 2. The magnitudes of corrosion current density ( j
corr
)
decreased for steel substrates exposed to the CO
2
saturated NaCl
electrolyte with increasing nanocomposite concentrations,
relative to the untreated corrosive chloride medium. This
process was initiated by steel surface coverage by protective
nanocomposite films and subsequent impedance of the corrosive
currents of chloride ions. This trend of j
corr
values is consistent
with corrosion inhibition in the presence of adsorbed nano-
composites on steel.
11
Magnitudes of j
corr
up to 855, 225, 180
and 88 mAcm
2
were recorded for 0, 5, 15 and 25 ppm nano-
composites. Corrosion inhibition could also have been fostered by
molecular adsorption due to the electron transfer and covalent
bond formation between partially occupied Fe
+2
orbitals.
9–11
Interfacial adsorption of protective nanocomposite films on steel
by chemisorption could have been possible via donor–acceptor
interactions. Values of E
corr
are also shifted to noble or positive
values with increasing nanocomposite concentrations, and this is
suggestive of the predominantly anodic dissolution mechanism
for steel substrates in the presence of the nanocomposite.
10
Enhanced corrosion inhibition was realized for the 25 ppm
CH(S)–GO nanocomposite (Z% = 89.7) compared to the same
concentration of its CH(S) graft polymer analogue (Z% = 70.7).
3.5. Analyses of metal surface morphologies after corrosion
tests
The results obtained from the two electrochemical techniques
have revealed inhibition in steel corrosion at inceased nano-
composite concentration. This led to in-depth analyses of
metallic surfaces after complete exposure to nanocomposite
doped CO
2
saturated saline medium at 60 1C for 24 h using
SEM and AFM. Fig. 6 depicts the SEM micrographs of untested
and abraded substrate (a) as well as treated steel substrates
within saline without (b) and with 25 ppm allyl sulfonate graft
chitosan CH(S) (c) and CH(S)–GO nanocomposites (d). Compared
to the unimpacted metallic surface, chloride-induced and CO
2
corrosion attacks had led to unimpeded surface damage, observed
as surface protrusions and grooves.
10
Therewerealsoevidenceof
significant pitting and formation of corrosion products and
crystalline carbonate scales due to CO
2
led steel dissolution within
the blank corrosive medium.
2,10
The presented surface morphology
also shows the extent of surface pits on steel at high magnification
after removing the adsorbed corrosion product/carbonate scales (e).
However, a significant improvement in corrosion inhibition is
observed in the presence of nanocomposites due to the formation
of protective inhibiting organic CH(S) and CH(S)–GO organic/
inorganic hybrid nanocomposite films on the steel substrate (f).
Film formation is confirmed in the presented EDS micro-
graphs; C, O and S are the elemental composition of the
adsorbed nanocomposite; Fe, Na and Cl originate from the base
metal and electrolyte, respectively. This also led to the reduction
in the surface roughness for steel in NaCl due to the reduced
corrosion attack and impedance of corrosive ion currents as
passive nanocomposite films formed on steel by molecular
adsorption.
2,10
The scales on the steel in CH(S) doped medium
are broken due to the excessive dehydration effect during surface
drying prior to imaging while the protective films in the presence
of the hybrid nanocomposite are more orderly formed and
morphologically compact.
Table 2 EIS and polarization parameters for metallic steel substrates exposed to CO
2
saturated NaCl solutions with CH(S)–GO nanocomposites and
CH(S) contents
System under study
EIS Potentiodynamic polarization
R
soln
(Ocm
2
)R
ct
(Ocm
2
) CPE, Y
o
(mFcm
2
s
(1ac)
)Z%E
corr
(V vs. Ref.) j
corr
(mAcm
2
)b
a
(mV dec
1
)b
c
(mV dec
1
)Z%
Blank (0 ppm) 2.3 61.4 658.8 — 0.68 855.0 97.3 147.5 —
25 ppm CH(S) 4.5 185.1 245.5 66.8 0.68 250.0 90.4 162.1 70.7
5 ppm CH(S)–GO 5.4 214.7 196.6 70.4 0.67 225.0 97.8 150.4 73.7
10 ppm CH(S)–GO 4.5 244.5 178.7 74.9 0.67 200.0 112.7 182.7 76.6
15 ppm CH(S)–GO 2.1 290.0 149.5 78.8 0.66 180.0 99.1 143.2 78.9
20 ppm CH(S)–GO 5.2 309.9 111.2 80.2 0.64 149.0 85.2 154.4 82.6
25 ppm CH(S)–GO 5.2 361.4 66.8 83.0 0.63 88.0 99.5 172.7 89.7
Values of goodness of fit (w
2
) are less than 10
4
; values of awithin this study are unity or close to unity. The magnitudes of corrosion inhibition
efficiency (Z%) were also computed from values of R
ct
and j
corr
obtained from the EIS and polarization techniques, respectively. For each technique,
these computed parameters were obtained in relative terms between steel substrates within the blank and in the presence of inhibitors.
2021 The Author(s). Published by the Royal Society of Chemistry Mater. Adv.,2021,2,16211634 | 1629
Materials Advances Paper

The results from SEM morphology were also complemented
by AFM surface analysis; similar trends in surface morphology
were recorded from both techniques as depicted in Fig. 6(g–j).
The roughness of the steel surface reduced upon addition of
the nanocomposite. The mean surface roughness (R
RMS
) of the
steel substrate within the undoped CO
2
saturated saline
electrolyte was 667 nm while 456 and 301 nm were recorded
for steel substrates within CH(S) and CH(S)–GO nanocomposite
doped medium. This trend shows evidence of corrosion inhibi-
tion in the presence of CH(S) and CH(S)–GO. A lower value of
surface roughness (114 nm) was recorded for the untested
surface, since it was carefully polished and has an even film-
free surface structure. The nanocomposite films are usually
multilayered and add extra roughness to corrosion impacted
surfaces; this trend could be attributed to the corrosion inhibition
in line with steel surface roughness lowering. This corrosion
inhibiting property of nanocomposite is consistent with its
adsorption at the Fe substrate/chloride electrolyte interface.
Corrosion inhibition is a consequence of mass transport
processes involving nanocomposite adsorption and its film
Fig. 6 SEM micrographs of precleaned untested (a) and tested (b) steel surfaces exposed to the CO
2
saturated NaCl electrolyte without corrosion
inhibitors, as well as tested steel strips within electrolytes containing the CH(S) (c) and CH(S)–GO nanocomposite (d) at 60 1C. Surface morphologies of
tested steel strips showing adsorbed corrosion product/carbonate scales (e) and adsorbed CH(S)/GO films (f) on steel substrates as well as corresponding
EDS micrographs showing selected elements (Fe, C, O, S, Na and Cl (Ka1)) from adsorbed CH(S)–GO nanocomposite films. Inset: surface morphology
showing the extent of surface pits (e) on steel at high magnification; Fe, Na and Cl originate from the base metal and electrolyte, respectively. The AFM
micrographs of precleaned untested (g) and tested (h) steel surfaces exposed to the CO
2
saturated NaCl electrolyte without corrosion inhibitors, as well
as tested steel strips within electrolytes containing CH(S) (i) and CH(S)–GO nanocomposite (j); the third column depicts surface line profiles (k) showing
the roughness variation for steel substrates exposed to these media.
1630 |Mater. Adv.,2021,2,16211634 2021 The Author(s). Published by the Royal Society of Chemistry
Paper Materials Advances

formationonsteel.
2,10
Molecular adsorption could be a physical
process or chemisorption as a result of electrostatic interactions
between charged surfaces and inhibitor molecules. The variation
of different surface parameters (texture, waviness and roughness)
could be seen on the last column of Fig. 6(k). These parameters
were profiled from the same AFM micrographs mapped in three-
dimensions. The surface of the steel substrate exposed to the
blank CO
2
saturated chloride electrolyte was significantly rough
and textured with uneven microstructural morphology due to
unhindered CO
2
-induced saline corrosion. This was not observed
in the presence of nanocomposites.Theprevalenceofiron
carbonate scale formations on the surface of the substrates is
due to the reaction between both ferrous and carbonate ions as
depicted in eqn (1).
10
Fe
2+
+CO
32
-FeCO
3
(1)
3.6. XPS analyses of adhering protective films on tested steel
surfaces
Evidence of metal–surface molecular adsorption by the hybrid
CH(S)–GO nanocomposite was probed by XPS technique.
Wide-scan XPS spectrograms of these adhering corrosion
inhibitor/corrosion product aggregates are presented in
Fig. 8, without (blank) and with the CH(S)–GO inhibitor in
the CO
2
saturated NaCl media. Varying chemical compositions
are revealed on both spectrograms within the range of binding
energy under study (0 to 1200 eV). Elemental components
consistent with hybrid nanocomposites are depicted in
Fig. 7 Nyquist (a) and polarization (b) curves for steel substrates exposed to CO
2
saturated NaCl media modified with different concentrations of hybrid
CH(S)–GO nanocomposites compared to the unmodified allyl sulphonate graft chitosan polymer (CH(S)).
Fig. 8 XPS spectra of adhering protective nanocomposite films/carbonate scales on steel substrates after exposure to CO
2
saturated NaCl at 60 1C
modified with allyl sulfonate graft chitosan/graphene oxide nanocomposites (CH(S)–GO); (a) wide scans with (green) and without (black) the CH(S)–GO
nanocomposite. High-resolution spectra (b–f) were collected for steel dispersed within the test corrosive medium modified only with the CH(S)–GO
nanocomposite.
2021 The Author(s). Published by the Royal Society of Chemistry Mater. Adv.,2021,2,16211634 | 1631
Materials Advances Paper

Fig. 8(a); this spectrogram shows core level peaks N 1s, S 2s,
O 1s, C 1s, etc.
9–11
This confirmed the adsorption of the
inhibitor aggregates as protective inhibitor films on the
charged metallic steel surface, and these films contain surface
functional groups containing oxygen (absorbed water and
hydroxyl/carboxyl groups) from the reduced GO nanosheets.
This carbon-based material is bound by the sp
2
network bearing
within its electrically conductive reduced GO network.
36
Without
this inhibitor nanocomposite, corrosion of steel also led to the
formation of corrosion product scales on the metallic surface
within the CO
2
saturated NaCl acidified medium due to the
accumulation of FeCO
3
scales at 60 1C.
9,35
Peaks consistent with
these carbonate scales could also be found at Fe 2p (at 709.5 eV),
C 1s (at 284.4 eV) and O 1 s (531.4 eV) while those related to the
corrosive electrolyte are located at 1071.2 eV (Na 1 s), 507.3 eV
(Na KLL), 270.1 eV (Cl 1s) and 198.8 eV (Cl 2p). The deconvoluted
high-resolution XPS spectra for selected elements were also
recorded in the presence of the CH(S)–GO nanocomposite; these
spectra are presented in Fig. 8(b–f). The C 1s XPS spectrogram (b)
shows triplet peaks and could be centers for metal adsorption.
The peak at 285.0 eV could be ascribed to the C–C bond from the
adsorbed hybrid protective nanocomposite film
39,40
while peaks
at 286.5 eV (C–N or C–O–C bond) and 287.9 eV (O–CQObond
from carbonyl) are also observed.
41
Peaks at 287.3 and 289.2 eV
could also be ascribed to FeCO
3
scales on steel. On the O 1s XPS
spectrogram (c), there are two sub-peaks at 530.5 and 531.5 eV
consistent with C–O and HO–CQO/or C–O–C, respectively.
9–11
Peaks at 530 eV could be assigned to metal–oxygen bonds from
metal hydrated oxide and carbonate scales.
10
Lu et al.
39
have
opined that the peak at 529.8 eV could be attributed to O
2
from
adhering carbonate scales. As presented in the S 2p spectrogram
(d), the S peak is deconvoluted into S2p
3/2
and S2p
1/2
doublets at
binding energy zoned between 160 and 171 eV. These peaks
could be due to the non-oxidized S sulphonate group, specifically
highlighting the C–S bond.
42,43
The single peak at 400 eV on the
N 1s spectrogram (e) is consistent with C–N bonds from the
carbon attached to the amine group abound deacetylated units
of D-glucosamine moieties or that of the acetylated unit of the
N-acetyl-D-glucosamine. These chemical groups were attached to
the adsorbed protective nanocomposite films on steel.
44
The Fe
2p spectrogram (f) shows low and high distinct spins from
p-orbital electrons. However, Fe 2p XPS spectrum (f) shows a
satellite peak at 721 eV while the other peaks with prominent
heights could be linked with metallic iron, Fe
2+
and/or Fe
3+
.
40
3.7. Surface contact angles of impacted steel surfaces
We have established from experimental evidence obtained
from surface analytical techniques that corrosion inhibition
by the CH(S)–GO nanocomposite was due to the metal–surface
molecular adsorption. To further confirm this, the surface
contact angle (y
o
w
) of each impacted steel surface was measured
in a view to assessing surface hydrophobicity using the sessile
drop method. Fig. 9(a) depicts the magnitudes of y
o
w
collected at
room temperature after the corrosion test, relative to untreated
metallic surfaces. While the unimpacted (untreated) surface
recorded a value of y
o
w
up to 391, the magnitude of this
parameter for treated metallic substrate within the blank CO
2
saturated NaCl stood at zero degree (01) due to surface evenness
in the presence of adsorbed FeCO
3
scales.
10
Without the
organic–inorganic hybrid inhibitor molecules within the corrodent,
steel significantly corroded. As observed in Fig. 6, this surface is
roughened with scale-rich and amorphous corrosion product
aggregates due to the impact of CO
2
corrosion and brine-
induced anodic dissolution. Higher values of y
o
w
(981) for
CH(S)–GO nanocomposite (1001for reduced GO) treated steel
relative to CH(S) (581) could be attributed to the formation of
hydrophobic graphene oxide films. These physically adsorbed
protective inhibitor films on steel reveal unsettled globular
shaped water droplets due to prevailing low surface energy
reduced GO nanosheet grafted hybrid nanocomposites.
45–47
Fig. 9 (a) Variation of values of aqueous contact-angles of non-impacted and impacted steel surfaces; (b) schematics showing the proposed
mechanism of corrosion inhibition by allyl sulfonate graft chitosan/graphene oxide (CH(S)–GO) nanocomposites adsorbed on the steel surface after
exposure to CO
2
saturated NaCl at 60 1C. At this temperature, the adsorption of the hybrid nanocomposite is also accompanied by FeCO
3
scaling and the
cathodic formation of HCO
3
(2H
2
CO
3
+2e

-H
2
+ 2HCO
3
) and CO
32
(2HCO
3
+2e

-H
2
+2CO
32
)at4opH o6.
10
The adsorption of the
CH(S)–GO nanocomposite significantly reduced anodic steel dissolution within the media, in turn forming chemical stable and hydrophobic protective
films. These compact films further obstruct the diffusion pathways of corrosive ions toward the metal surfaces.
8–10
1632 |Mater. Adv.,2021,2,16211634 2021 The Author(s). Published by the Royal Society of Chemistry
Paper Materials Advances

The trend of y
o
w
values in Fig. 9 shows a correlation between
surface wettability and molecular adsorption in the presence of
nanocomposites with significantly reduced solid–liquid contact
area.
3.8. Proposed mechanism of corrosion inhibition by hybrid
nanocomposites
Experimental evidence has revealed severe metal surface pits as
consequences of synergistic chloride and CO
2
corrosion attacks
as presented in the SEM and AFM micrographs (Fig. 6). These
anodic dissolution episodes are isolated and localized without
the CH(S)–GO nanocomposite within the corrosion media.
However, these surface events differ significantly in the
presence of corrosion inhibitor nanocomposites after their
adsorption on steel.
10–12
This complex adsorption mechanism
is depicted in the schematics shown in Fig. 9(b). It shows the
proposed monolayer adsorption of the allyl sulfonate graft
chitosan/graphene oxide (CH(S)–GO) nanocomposite on the
steel surface, leading to its corrosion inhibition in CO
2
saturated
NaCl at 60 1C. At this temperature, the adsorption of the
nanocomposites is also accompanied by FeCO
3
(eqn (1)) scaling
and two cathodic reactions involving the formation of carbonate
and bicarbonates.
10,11
Weak carbonic acid was also formed when
the CO
2
gas was dissolved within the aqueous medium (eqn (2)),
leading to lower pH values (eqn (3)). This acid further initiated
steel corrosion, leading to the anodic reaction that involved Fe
2+
ions going into the medium (eqn (4)).
10
The adsorption of the CH(S)–GO nanocomposites significantly
reduced anodic steel dissolution, in turn forming stable and
hydrophobic protective films. The presence of these compact
films further obstructed the diffusion pathways of corrosive ions
toward the metal surfaces. These CH(S)–GO nanocomposites
covered the metal surfaces by physisorption and could also have
formed protective surface films due to donor–acceptor electron
exchanges. These electron exchanges originate from metal-
inhibitor type reactions leading to the electron pair interactions
between the chitosanic moiety and vacant 3d-orbitals of the
metallic steel substrate.
10–13
Here, the chemical structure of the
nanocomposite comes into play. The grafted chitosanic copoly-
mer comprises of long polymeric chain bound lone pair electrons
that can act as metal–surface bonding sites for strong coordina-
tion bond formation. As presented in the results obtained from
the XPS technique, these protective (CH(S)–GO) nanocomposite
films on steel contain hybrid polymeric graphene oxide and
chitosanic functionalities required for stable corrosion-
resistance, relative to unmodified allyl sulphonate graft chitosan
(CH(S)). If adsorbed monolayers of polymer CH(S) films could
significantly distorted anodic or cathodic reaction, those of poly-
meric nanocomposites would sustain an enhanced degree of
surface protection against corrosion due to inherent rGO
nanosheets within the composite. Corrosion inhibition was
due to the synergistic effects of the individual polymeric
components.
CO
2(g)
2CO
2(aq)
(2)
CO
2(aq)
+H
2
O
(l)
2H
2
CO
3(aq)
(3)
Fe
2+
+2e

-Fe (4)
4. Conclusions
In this study, allyl sulfonate graft chitosan (CH(S)) was synthesized
by an acetic-acid catalyzed reaction involving chitosan (CH) and
allyl sulfonate in an alkaline reaction bath. CH(S) was subse-
quently grafted onto graphene oxide nanosheets. The resultant
organic/inorganic hybrid (CH(S)–GO) nanocomposite was then
characterized using appropriate techniques and utilized as a
corrosion inhibitor for an X70 pipeline steel substrate in a CO
2
saturated NaCl electrolyte. Significant corrosion reduction was
realized in the presence of the hybrid (CH(S)–GO) nanocomposite.
Corrosion inhibition was attributed to the molecular adsorption
and formation of protective nanocomposite films on the steel
surface. However, dissolution of steel in the nanocomposite
doped corrosive electrolyte exhibited a predominantly anodic
kinetics. Evidence of molecular adsorption was elucidated by
means of surface analytical techniques. Morphological and com-
positional results from SEM (including AFM) and XPS techniques
revealedthepresenceofadsorbednanocomposite/carbonate scale
aggregates on less corroded steel surfaces. The degree of corrosion
inhibition between the (CH(S)–GO) nanocomposite and its CH(S)
precursor has been experimentally established, and superior sur-
face protection is revealed in the presence of the nanocomposite.
These physically adsorbed protective nanocomposite films on
steel contributed to enhanced surface hydrophobicity due to the
prevailing low surface energy instigated by the reduced GO
nanosheet contents. While the CH(S) copolymer analogue con-
tributed to significant surface coverage, the (CH(S)–GO) polymer
nanocomposite adsorption accorded a broad metal–surface pro-
tection, hence, was a more effective corrosion inhibitor. The
CH(S)–GO polymer nanocomposite offered sustained surface
protection against corrosion due to the synergistic effects of its
individual polymer components. Without the hybrid nanocompo-
site, anodic steel corrosion was significant within the undoped
electrolyte, and corrosion was attributed to the irreversible action
of the CO
2
saturated chloride solutions. Before corrosion tests, the
pipeline steel substrates utilized within this study was character-
ized by means of SEM and EBSD techniques. The microstructure
ofpipelinesteelsubstratesutilizedwithinthisstudywaschar-
acterized by using the EBSD technique. Mostly refined bainitic-
ferrite grains with orientation deviation towards [111]||ND and
[011]||ND directions were observed across the steel structure.
Also, the steel displayed significant proportion of deformed
regions and increased intensity of grain misorientation.
Conflicts of interest
The authors declare no conflict of interest.
Acknowledgements
The University of Saskatchewan is acknowledged for providing
the facilities for this study. This experimental work was
2021 The Author(s). Published by the Royal Society of Chemistry Mater. Adv.,2021,2,16211634 | 1633
Materials Advances Paper

initiated and completed while UE was still at the Department of
Mechanical Engineering, University of Saskatchewan, Saskatch-
ewan, Canada.
References
1 U. Eduok, E. Jossou, A. Tiamiyu, J. Omale and J. Szpunar,
Ind. Eng. Chem. Res., 2017, 56, 5586–5597.
2 U. Eduok, E. Jossou and J. Szpunar, J. Mol. Liq., 2017, 241,
684–693.
3 M. E. Olvera-Martı
´nez, J. Mendoza-Flores and J. Genesca,
J. Loss Prev. Process Ind., 2015, 35, 19–28.
4 E. Stupnisek- Lisac, S. Podbrscek and T. Soric, J. Appl.
Electrochem., 1994, 24, 779–784.
5 N. O. Obi-Egbedi, I. B. Obot and M. I. El-Khaiary, J. Mol.
Struct., 2011, 1002, 86–96.
6 J. Wang, D. Liu, S. Cao, S. Pan, H. Luo, T. Wang, H. Ding,
B. B. Mamba and J. Gui, J. Mol. Liq., 2020, 312, 113436.
7 I. B. Obot and U. M. Eduok, J. Mol. Liq., 2017, 246, 66–90.
8 Y. El Aoufir, R. Aslam, F. Lazrak, R. Marzouki, S. Kaya,
S. Skal, A. Ghanimi, I. H. Ali, A. Guenbour, H. Lgaz and
I. M. Chung, J. Mol. Liq., 2020, 303, 112631.
9 U. Eduok, E. Ohaeri, J. Szpunar and I. Akpan, J. Mol. Liq.,
2020, 315, 113772.
10 U. Eduok, E. Ohaeri and J. Szpunar, Ind. Eng. Chem. Res.,
2019, 58, 7179–7192.
11 U. Eduok, E. Ohaeri and J. Szpunar, Electrochim. Acta, 2018,
278, 302–312.
12 U. Eduok and J. Szpunar, ECS Meeting Abstracts, 2019,
8, 853.
13 M. Srivastava, S. K. Srivastava, Nikhil, G. Ji and R. Prakash,
Int. J. Biol. Macromol., 2019, 140, 177–187.
14 D. D. Divakar, N. T. Jastaniyah, H. G. Altamimi,
Y. O. Alnakhli, Muzaheed, A. A. Alkheraif and S. Haleem,
Int. J. Biol. Macromol., 2018, 108, 790–797.
15 E. Badr, H. H. H. Hefni, S. H. Shafek and S. M. Shaban, Int.
J. Biol. Macromol., 2020, 157, 187–201.
16 R. K. Gupta, M. Malviya, K. R. Ansari, H. Lgaz,
D. S. Chauhan and M. A. Quraishi, Mater. Chem. Phys.,
2019, 236, 121727.
17 H. J. Majidi, A. Mirzaee, S. M. Jafari, M. Amiri,
M. Shahrousvand and A. Babaei, Int. J. Biol. Macromol.,
2020, 148, 1190–1200.
18 S. Singh, G. Singh, N. Bala and K. Aggarwa, Int. J. Biol.
Macromol., 2020, 151, 519–528.
19 A. B. Ikhe, A. B. Kale, J. Jeong, M. J. Reece, S.-H. Choi and
M. Pyo, Corros. Sci., 2016, 109, 238–245.
20 E. M. Fayyad, K. K. Sadasivuni, D. Ponnamma and
M. A. A. Al-Maadeed, Carbohydr. Polym., 2016, 151, 871–878.
21 N. Kirkland, T. Schiller, N. Medhekar and N. Birbilis, Corros.
Sci., 2012, 56, 1–4.
22 D. Prasai, J. C. Tuberquia, R. R. Harl, G. K. Jennings and
K. I. Bolotin, ACS Nano, 2012, 6, 1102–1108.
23 H. Tian, W. Li, B. Hou and D. Wang, Corros. Sci., 2017, 117,
43–48.
24 W. Bai, Q. Sheng and J. Zheng, Talanta, 2016, 150, 302–309.
25 K. Haruna, T. A. Saleh, I. B. Obot and S. A. Umoren, Prog.
Org. Coat., 2019, 128, 157–167.
26 S. J. Garcia, T. A. Markley, J. M. C. Mol and A. E. Hughes,
Corros. Sci., 2013, 69, 346–358.
27 ASTM G3 - 89 (2010) Standard Practice for Conventions
Applicable to Electrochemical Measurements in Corrosion
Testing. (https://www.astm.org/DATABASE.CART/HISTORI
CAL/G3-89R10.htm).
28 S. Vervynckt, K. Verbeken, B. Lopez and J. J. Jonas, Int.
Mater. Rev., 2012, 57, 187–207.
29 E. Ohaeri, J. Omale, A. Tiamiyu, K. M. M. Rahaman and
J. Szpunar, J. Mater. Eng. Perform., 2018, 27, 4533–4547.
30 M. Jiang, K. Wang, J. F. Kennedy, J. Nie, Q. Yu and G. Ma,
Int. J. Biol. Macromol., 2010, 47, 696–699.
31 Y. Wu, Y. L. Zheng, C. C. Wang, J. H. Hu and S. K. Fu,
Carbohydr. Polym., 2005, 59, 165–171.
32 R. A. Ahmed, R. A. Farghali and A. M. Fekry, Int.
J. Electrochem. Sci., 2012, 7, 7270–7282.
33 C. J. E. De Souza, M. M. Pereira and H. S. Mansur, J. Mater.
Sci. Mater. Med., 2009, 20, 553–561.
34 E. M. Fayyad, K. K. Sadasivuni, D. Ponnamma and
M. A. A. Al-Maadeed, Carbohydr. Polym., 2016, 151, 871–878.
35 D. He, Z. Peng, W. Gong, Y. Luo, P. Zhao and L. Kong, RSC
Adv., 2015, 5, 11966–11972.
36 L. Stobinski, B. Lesiak, A. Malolepszy, M. Mazurkiewicz,
B. Mierzwa, J. Zemek, P. Jiricek and I. Bieloshapka,
J. Electron Spectrosc., 2014, 195, 145–154.
37 J. Zhang, H. Yang, G. Shen, P. Cheng, J. Zhang and S. Guo,
Chem. Commun., 2010, 46, 1112–1114.
38 D. He, Z. Peng, W. Gong, Y. Luo, P. Zhao and L. Kong, RSC
Adv., 2015, 5, 11966–11972.
39 Y. Lu, H. Jing, Y. Han, Z. Feng and L. Xu, Appl. Surf. Sci.,
2016, 389, 609–611.
40 N. Z. N. Hashima, E. H. Anouar, K. Kassim, H. M. Zaki,
A. I. Alharthib and Z. Embong, Appl. Surf. Sci., 2019, 476,
861–877.
41 D. H. Wang, Y. Hu, J. J. Zhao, L. L. Zeng, X. M. Tao, W. Chen
and H. Holey, J. Mater. Chem. A, 2014, 2, 17415–17420.
42 M. Ahangar, M. Izadi, T. Shahrabi and I. Mohammadi,
J. Mol. Liq., 2020, 314, 113617.
43 A. Abdul Razzaq, Y. Yao, R. Shah, P. Qi, L. Miao, M. Chen,
X. Zhao, Y. Peng and Z. Deng, Energy Storage Mater, 2019,
16, 194–202.
44 S. B. Jiang, L. H. Jiang, Z. Y. Wang, M. Jin, S. Bai, S. Song and
X. Yan, Construct. Build. Mater., 2017, 150, 238–247.
45 T. Ghosh, P. Bardhan, M. Mandal and N. Karak, Mater. Sci.
Eng., C, 2019, 105, 110055.
46 E. Udabe, M. Forsyth, A. Somers and D. Mecerreyes, Mater.
Adv., 2020, 1, 584–589.
47 A. Ul-Hamid, Mater. Adv., 2020, 1, 1012–1037.
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